Cabbage sprouts have dark green, floppy leaves that look like those of pak choi, choi sum and some other types of brassica; but the core looks like a small, elongated Brussels sprout.
Although it's a delicious vegetable - it tastes like broccoli stems with a hint of bitterness - the cabbage sprout doesn't seem very popular; the only time I've ever seen it on menus has been in Thai restaurants. The fresh vegetable is equally elusive - I've only spotted it in markets specialising in Southeast Asian produce. If you do find some, check the vegetables carefully because the loose leaves can harbour bugs and worms. Buy small- to medium-sized specimens that feel heavy for their size, meaning less leaf and more core. The leaves should be dark and unshrivelled.
According to the University of Illinois Extension website, cabbage sprouts are a secondary harvest. They grow on the stumps of the stem after the head cabbage has been cut off.
You can prepare cabbage sprouts in any of the ways you would Brussels sprouts. I favour cooking them with salted fish and fish sauce.
Cut the cabbage sprouts in half lengthwise (some of the leaves will fall off, but that's fine), then rinse them well and drain in a colander. Cut a small, meaty chunk of Chinese salted fish into 5mm cubes, rinse them briefly, then pat them dry with paper towels. Pour oil to a depth of about 1cm into a wok, add the salted fish and stir fry until the pieces are slightly brown and the pungent odour is released. Remove the fish from the wok, leaving behind most of the oil. Add the halved cabbage sprouts to the wok and stir-fry over a high flame, letting them char in spots. Add sliced garlic and stir-fry for about 30 seconds, then drizzle in some fish sauce that's been mixed with a little sugar. Stir constantly until the cabbage sprouts are almost al dente then return the fish to the wok and stir-fry for another minute.